The present invention relates to a rotation mechanism for a rotatable seat for vehicles for convenience of entry into and exit from a vehicle.
More specifically, the present invention relates to a rotation mechanism for a rotatable seat which allows the seat to be pivotable between a normal forwardly directed position and a pivoted position directed toward a door opening for providing easy entry and exit of passengers into and from the vehicle's seat.
For easy entry and exit of the passengers into and from the vehicle's seat, recently rotatable seats for use on the automotive vehicles have been developed, which are generally provided with a rotation mechanism including a latch member to prevent the seat from being free to be rotated with respect to a vehicle's floor when the seat is in the normally forwardly directed position.
A typical rotation mechanism for a rotatable seat has, as shown in FIG. 5 and FIG. 6, a lower rail 1 secured to a floor of a vehicle, an upper rail 2 slidable forwardly and backwardly relative to the lower rail 1, a lower guide rail 4 secured to the upper rail 2 and having a cylindrical flange 3, an upper guide rail 5 rotatable around the flange 3 and having a lock lever 6 for restricting the rotation of the upper guide rail 5 against the lower guide rail 4, in which construction a seat cushion (not illustrated) is mounted to the upper guide rail 5. In FIG. 6, reference numeral 7 denotes a ball for facilitating relative rotation between both of the guide rails 4 and 5, and 8 denotes a shoe secured to an inverted U-shaped edge at the top end of the flange 3.
Upon use, after detecting the parking or neutral position of a shift lever or confirming the detection of the off position of an ignition key, the upper guide rail 5 is manually rotated relative to the lower guide rail 4 by the operation of the lock lever 6 to turn the seat toward the door opening to facilitate getting in and out of a passenger.
Examples of such the rotation mechanism for rotatable seat are disclosed, for example, in Japanese Patent Laid-Open Publication Sho 63-141841 (1988), Japanese Patent Laid-Open Publications Sho 61-163034 (1986) and Sho 61-196833 (1986). These prior art examples teach that the operation of the lock lever is enabled in accordance with a signal from the shift lever or the ignition key operation, and that the solenoid or the actuator is utilized for the operation control of the lock lever.
However, in the prior art examples described above, when an external force higher than the operation force for a manual operation of the lock lever is exerted on the lock lever, the external force is directedly inputted into the solenoid or the actuator, which may undesirably lead to destruction of the solenoid or the actuator.